Mitsubishi srk40hg-s compressor problems...

[Topsie]

Hi, new to the forum so apologies if I'm posting in the wrong place!

Basically, after charging my newly installed but 2nd hand srk40hg-s, the unit wasn't cooling or heating. After a bit of a panic I realised I'd shut the 3-way service valve, assuming it would isolate the service connection!

Anyways, the compressor was working fine before I opened the service valve, with the system pumping down every 30 seconds or so. I opened the service valve and now the compressor won't start, it just "buzzes" for 3-4 seconds.

My first thought is the thermal motor protection, but according to the manual this will throw an error code, which it isn't, the compressor however is nice and warm once it's been trying to start for while...

I'm hoping its a component and not the compressor, but I'm unsure of how to go about diagnosing the problem...

Any help is greatly appreciated!

Nick

[Brian_UK]

Switch it off for 24 hours and let the compressor cool down.

If the unit has a crankcase heater so much the better.

It's possible that you have flooded the compressor which is why it wouldn't start.

[Topsie]

Tried leaving it overnight to no avail...

Flooded compressor sounds plausible, only because it only stopped working when I opened the service valve! I'm assuming the only way to clear the compressor is to recover the gas?

[Topsie]

Oh and no crankcase heater shown in the wiring diagram!

[marc5180]

Have you checked if you have the correct power at the compressor when it is "buzzing".

[install monkey]

http://www.mhi-systems.ru/uploads/pdf/SRK-HG-S.pdf
service manual- 1 phase system, no crankcase htr, check capacitor is within 10% of uf rating

[install monkey]

when u install a split- you pressure test the system with the service valves closed- upto 40 bar of nitrogen, then vac system to under 3 torr, then add any additional charge depending on the length of run, then open both service valves suction, liq- refit the caps tightly then remove your gauges

[Topsie]

Okay I've got more information. The system was overcharged, 1.5kg instead of 1.15 kg (for a 15m run) which is my fault, misread the charge...

This makes the flooded compressor more plausible, but at the same time shouldn't the refrigerant boil off and settle elsewhere?

Going to test the voltage to the compressor terminals and the capacitor tonight, as well as recover and re-gas with the correct weight....

[Topsie]

Okay, gas recovered and compressor motor capacitor tested good... This leaves me with the compressor motor windings to test and the motor protection to test... Do split systems have HP/LP pressure switches? I can't see it on the wiring diagram but it doesn't show control and indication, could it be running for 3-4 seconds and tripping on HP or LP?

I haven't charged he system again yet, I'm trying to get to the bottom of the compressor fault first...

[frank]

Do split systems have HP/LP pressure switches? I can't see it on the wiring diagram but it doesn't show control and indication, could it be running for 3-4 seconds and tripping on HP or LP?

If you look on page 20 of the manual IM posted, the High pressure control is done by the electronics - same as for low pressure (Frost Protection)

[Topsie]

So could the humming be he compressor running for short periods of time and then tripping out on LP? (As there is no gas in the system)

Electrically, the compressor is sound. Resistance across the 3 terminals on the compressor are what I'd expect, 2ohm, 3ohm and 6ohm. Capacitor is bang on 30uF and when trying to start the motor I'm getting 6-7 amps drawn on each cable, 3amps on the neutral phase returning to the terminal block.

I'm apprehensive to charge the system again without some indication that the compressor is ok..personally, I think it's seized. After 4-5 times trying to run the compressor housing is getting hot. Oh and the thermal cut out is also showing good continuity...

I have the manual but I guess I lack the experience to interpret...

Help! Lol

[install monkey]

no pressure switches on it- hi or low- only safety device is motor klixon- check the comp name plate to see the lra - locked rotor amps, prob prob 20amp cooling should pull 3.6amp heating 5.2 amp- once lev has stabilised ( couple of mins)
if it pulls 5 amp and cuts out on overload then weak overload, if it pulls 20 ish amp then siezed, could pull 10amp and be siezing if the current increases

[Topsie]

It's only pulling max 7amps, all had me very confused... I'll try and get to the name plate tomorrow and check lra.

I don't think it's cutting out on overload because, according to the manual I would get an error signal, or am I looking at the thermal overload protection?

[install monkey]

if your getting continuos voltage down the comp leads then its your klixxon- when it cuts out the bi metal strip will cool down and youll hear it click when it resets

[Topsie]

That's another test for tomorrow then... Is it possible that it's just a weak klixxon?

[frank]

Bypass the klixon to find out

[install monkey]

whilst continuously monitering the running current

Bypass the klixon to find out

[Topsie]

Just ran the compressor without the klixxon and it continued running, I didn't measure the running current (as I've just read this thread) but I only let it run for 10 seconds or so, as there is no refrigerant charge at the moment.

Tomorrow I'll charge the system and measure the running current while the compressor is running. It's worth noting the 'buzzing' went away once the compressor was running for little while. If the klixxon was at fault it was opening on current, not heat as I ran the compressor with the klixxon away from the compressor and it still tripped.

More to follow, but I'm hopeful!....

[install monkey]

get some gas in it before u run it;)

[Topsie]

Might just take this moment to say thanks for the help, might even be a pack of biscuits in this lol! But seriously, much appreciated.

[install monkey]

jaffa cakes:p haha

[Topsie]

Klixxon out of circuit, monitored current drawn when charged and running (3.2amps) aaaand., it got really hot and tripped the RCD..... Yeah it's f**ked lol! Still appreciate all the help though :)

[install monkey]

you tested the winding resistance 3,7,8 ohm did you megger each comp pin to earth (with comp leads disconnected) to ensure insulation is over 1 meg ohm- rcds protect from earth leakage- as you were monitering current draw there was no sign of over current

[Topsie]

Don't have a merger to hand, but the compressor was waaaaay to hot, there was no continuity between terminals and earth but I've no doubt if I checked IR it would be pretty poor... Also with the LP gauge connected to the service valve there was no movement whatsoever, must of been trout winding all along.... I guess that's what you get for trying to cheap out on a second hand unit :(